Reality hit Sylvia Ann Hewlett in 1977 when, at the age of 31, she was an assistant professor of economics at Barnard College in New York, and gave birth to her first child.

She was not entitled to maternity leave, paid or unpaid, and had to return to work 10 days after the birth. Even though she worked for a bastion of intellectual feminism, she found that, as a practical matter, there were no supports for her efforts to combine a career with motherhood.

In the years that followed she was denied tenure by Columbia University, despite a unanimous recommendation by her department and Barnard's tenure committee, and eventually became director of the Economic Policy Council, the prestigious gathering of leaders of labor, industry and academe.

With grants from the Ford and Rockefeller foundations, she set up a policy panel to examine women and work in America and compare the situation here with those faced by women in Sweden, Italy, France and her native England.

The result of her research and analysis is "A Lesser Life -- the Myth of Women's Liberation in America," soon to be published by William Morrow & Co. It is an eye-opening and enormously provocative look at the historical forces that have trapped modern women in a daily grind of trying to reconcile motherhood and work in a country with one of the highest divorce rates and weakest family support systems of any industrial nation.

"Women of my age in America," she writes, "are at the mercy of two powerful and antagonistic traditions. The first is the ultradomestic fifties with its powerful cult of motherhood; the other is the strident feminism of the seventies with its attempt to clone the male competitive model . . . .

"An American woman trying to fulfill the demands of both traditions is obviously in something of a dilemma . . . . And her attempt to manage both roles is further undermined by the fact that American society, having produced the strongest and most antithetical dual roles for women, has left them with the weakest support systems with which to mediate these roles.

"Successive administrations have repeatedly failed to provide the maternity leaves and child-care facilities so taken for granted by working parents in other advanced countries."

The result, she argues, is that women are forced into a succession of bad compromises when they start having children. She looks at the appallingly low numbers of tenured women: 4.2 percent at Harvard, 2.6 percent at Stanford in the early 1980s.

"This situation cannot be blamed on a scarcity of qualified women; the pipeline is full of women . . . . " she writes. "At least some of these women do not make it to the top of their profession because they have the audacity to become mothers and proceed to raise children in a work environment that makes few concessions to maternal roles . . . .

"The end result is that professional women with children find their energies hopelessly stretched in their mid-thirties, precisely the time when academic careers (and many other careers) are either made or broken."

As for nonprofessional women, they "were left behind to cope with deteriorating economic and social realities," she writes. "The economic reality is that most women still earn very little on their own, and the social reality is that contemporary women are more likely to be on their own."

"American women are locked into a no-win situation," she declares, because they have lost the financial security of marriage and failed to improve their earning power.

Women in Sweden, Italy, England and France are doing better, she reports, and they have narrowed the wage gap, where we have not. Swedish women earned 81 percent of what men earned in 1980, up from 71 percent in 1970. She notes that the wage gap also has narrowed substantially in Italy, West Germany, France and Denmark.

"It is no coincidence that the country with the most developed benefits and services for working women -- Sweden -- is also the country with the smallest wage gap, while the country with the least developed benefits and services -- the United States -- is also the country with one of the largest wage gaps," she points out.

The antidiscrimination efforts of the 1970s had little impact on the wage gap, she writes, because they failed to address the double burden of women's lives.

For this, she faults the women's movement whose leaders were so caught up in the issues of equal rights that they ignored or downplayed the most critical issue: reconciling motherhood and work. The vacuum they left on family concerns ended up being filled by traditionalists who failed to understand that most modern women work because they have to.